DAVIS GroWeather Console - Manual (Page 14)

Weather Conditions Measured/Calculated
GroWeather Manual Page 7
Growing Degree-Days (Heat Units)
Because temperature plays an important part in the rate of development of
plants and many pests (especially insects) a measurement which takes into
account the accumulation of heat with passing time is necessary to predict mat-
uration. Growing degree-days provide a measure for calculating the effect of
temperature on the development of plants and/or pests. One degree-day is the
amount of heat which accumulates when the temperature remains one degree
above the base developmental threshold (base threshold) for 24 hours. One
degree day is
also the amount of heat which accumulates when the temperature
remains 24˚ above the base threshold for 1 hour.
In order to use degree-days effectively, you must know the developmental
threshold(s) for the desired crop or pest. The base developmental threshold is
the temperature at and below which development stops. Above the base
threshold development increases until temperature reaches the upper thresh-
old, over which development rate decreases.
Note: The GroWeatherLink Software enables you to calculate, display, and print crop and pest-specific
degree-day totals. See “Optional Accessories” on page 2 for more details.
Unlike strict time predictions of plant/pest development, degree-day predic-
tions hold true regardless of location or temperature fluctuations. As long as
you know the number of degree-days necessary for plant/pest development,
you may use degree-days as an accurate predictor. For example, you may
know that it takes, in general, three weeks for a specific pest to develop. What
you will find, however, is that the pest may take 4 weeks to develop in cooler
weather and only 2 weeks to develop in warmer weather. The time prediction
can be off by up to a week in this example, while the degree-day prediction
should result in far greater accuracy.
The GroWeather uses the temperature reading in conjunction with the base and
upper thresholds which you set (see “Setting Thresholds” on page 24) to calcu-
late degree-days. The GroWeather keeps a running total of the accumulating
“degree-minutes” and “degree-seconds” to provide the most accurate degree-
day information possible. Keep in mind that local variations in terrain, vegeta-
tion, and elevation can make a significant difference in temperature readings,
so you should endeavor to place the temperature sensor in the same location as
the plant/pest.
• “Daily” Degree-Days Sum (AutoClear)
• Total Degree-Days for the period (Alarm: High)
• Average Degree-Days per day over the period